In the first instance of a human-to-plant pathogen transfer, a bacterium related to the one that causes pimples has been found on a common grapevine.

Grapevines can't grow zits, but they do carry bacteria related to the acne-causing pathogen found on human skin, according to a new report describing the first known case of a bacterium transferring from a human to a plant.

The bacteria species Propionibacterium acnesplagues the skin of humans worldwide, and has always been thought of as an exclusively human-seeking pathogen. So when researchers based at the Research and Innovation Center – Fondazione Edmund Mach in Italy analyzed bacterial colonies growing on the common grapevine Vitis vinifera in Northeast Italy, they were surprised to find a previously unknown relative of P. acnes living in the bark of the plant.

Based on the genetic makeup of the new bacterium, as compared to other related strains, and the evolutionary history of those other strains, the researchers estimate farmers transferred the pathogen to the plants roughly 7,000 years ago. Since then, the bacterium has become entirely plant-adapted, and it can no longer return to its original human host, the team reported Tuesday (Feb. 18) in the journal Molecular Biology and Evolution. [5 Ways Gut Bacteria Affect Your Health]

"It has never been discovered that a human bacterium could be adapted to be the guest of a plant cell," study co-author Andrea Campisano told Live Science. "This is the first time that it is described, and it finally answers the question of whether it is possible or not."

The team named the new bacterium P. Zappae after the late Italian-American musician Frank Zappa, because they believe that Zappa, like the finding, was "unconventional."

"The fact that it was so unusual made us think of someone as unusual and eclectic as Frank Zappa, who was a surprising person," Campisano said. "And we wanted to honor him on the 20th anniversary of his death." Zappa died on Dec. 4, 1993.

The word "zappa" also means "hoe" in Italian, further justifying the name for an agriculturally related bacterium.

Plants containing P. Zappae were completely healthy, suggesting the bacterium has no negative effects on the plants, and may even benefit the grapevines, the team says. Plants, like humans, require a certain balance of microbes to remain physiologically healthy, Campisano said.

The researchers hope their discovery will inform the development of new microbial treatments that could potentially boost the health of grapevines and other commercially important crops, similar to how probiotics boost human health, Campisano said.

Though this is the first example of a human-to-plant pathogen transfer, the team thinks the same bacterium may live in other domesticated plants, and that other types of bacteria may also have transferred from humans to plants, Campisano said.

The team next hopess to analyze the entire genome of P. Zappae to understand how the human-to-plant transfer changes bacterial DNA, and also hopes to determine whether the bacterium benefits the plants, Campisano told Live Science.